Bump sphinxcontrib-serializinghtml from 1.1.5 to 1.1.9

Bumps [sphinxcontrib-serializinghtml](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml) from 1.1.5 to 1.1.9.
- [Release notes](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/releases)
- [Changelog](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/blob/master/CHANGES)
- [Commits](sphinx-doc/sphinxcontrib-serializinghtml@1.1.5...1.1.9)

---
updated-dependencies:
- dependency-name: sphinxcontrib-serializinghtml
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

constraints.txt

@@ -200,7 +200,7 @@ sphinxcontrib-jsmath==1.0.1
     # via sphinx
 sphinxcontrib-qthelp==1.0.3
     # via sphinx
-sphinxcontrib-serializinghtml==1.1.5
+sphinxcontrib-serializinghtml==1.1.9
     # via sphinx
 sspilib==0.1.0
     # via pyspnego